Ronald Strahan | 7/26/2016 6:29:06 PM
Chamberbitter (Phyllanthus urinaria), also called gripeweed or leaf flower, is a highly invasive summer annual broadleaf that has become a serious weed of nurseries and landscape beds in Louisiana over the past 15 years. It is believed that the weed originated in tropical Asia, but it has become problematic across the southeastern United States from Virginia to Texas.
The weed is characterized by leaves arranged in two rows on alternate branchlets, superficially resembling mimosa seedlings. However, the most common distinguishing feature is fruit attached directly to the underneath sides of branches. Reproduction is by seeds, which explode outward from maturing fruit onto surrounding areas. Seeds require soil temperatures above 75 degrees to germinate, and plants persist into late fall until a killing frost. Chamberbitter grows 1 to 2 feet in height and produces thousands of seeds. The weed is unsightly in flower beds and is costly to control in nurseries.
Chamberbitter control in landscape beds and nurseries
Because few selective postemergence options are available for controlling broadleaves infesting ornamentals, preemergence herbicides are the backbone of weed management in flower beds and nurseries. Unfortunately, chamberbitter responds erratically to most preemergence herbicides labeled for ornamentals. However, a few preemergence herbicides provide at least suppression of the weed. Herbicides that contain oxyfluorfen (Rout, OH2 and others), flumioxazin (Sure Guard and Broadstar) and isoxaben (Snapshot, Gallery) are useful in reducing chamberbitter populations in perennial groundcovers and woody plants. Dimethenamid-containing herbicides (Free Hand and Tower) can be moderately effective in bedding plants. Always follow product labels and precautions when using herbicides in and around ornamentals.
With all preemergence herbicides, it is important to apply them before weeds germinate.
Chamberbitter is a tropical plant that starts germinating as temperatures warm in the springtime, usually late April, so apply preemergence herbicides accordingly. Re-apply as directed by the product label. In landscape beds, a good thick mulch will also help suppress chamberbitter emergence, especially when used in conjunction with an effective preemergence herbicide.
Since chamberbitter is a prolific seed producer, it is extremely important to not allow emerged plants to produce seed and add more seed to the soil weed seed bank. Either hand-remove the weed or apply a non-selective herbicide such as glyphosate to destroy populations before they have a chance to produce seeds.
Chamberbitter is an extremely difficult weed to manage in ornamental settings. It will take an integrated management approach that includes mulch and preemergence herbicides along with frequent hand weeding and glyphosate applications to reduce populations in nurseries and landscape beds.
Ron Strahan is a weed scientist and associate professor in the School of Plant, Environmental and Soil Sciences.
Fruit on chamberbitter. Photo by Ron Strahan
Chamberbitter seed capsules are located on the underside of leaves. Photo by Ron Strahan